Publikace ÚTF

Limb-darkening measurements for a cool red giant in microlensing

Zub M., Heyrovský D., et al.

Aims. We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event that exhibits clear
extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of
their source star, as shown in this study.
Methods. Our dense photometric coverage of the overall light curve and a proper microlensing modelling allow us to derive measurements of
the OGLE 2004-BLG-482source star’s linear limb-darkening coefficients in three bands, including standard Johnson-Cousins I and R, as well as
in a broad clear filter. In particular, we discuss in detail the problems of multi-band and multi-site modelling on the expected precision of our
results. We also obtained high-resolution UVES spectra as part of a ToO programme at ESO VLT, from which we derive the source star’s precise
fundamental parameters.
Results. From the high-resolution UVES spectra, we find that OGLE 2004-BLG-482’s source star is a red giant of MK type a bit later than M3,
with Teff = 3667±150 K, log g = 2.1±1.0 and an assumed solar metallicity. This is confirmed by an OGLE calibrated colour−magnitude diagram.
We then obtain from a detailed microlensing modelling of the light curve linear limb-darkening coefficients that we compare to model-atmosphere
predictions available in the literature, and find a very good agreement for the I and R bands. In addition, we perform a similar analysis using an
alternative description of limb darkening based on a principal component analysis of ATLAS limb-darkening profiles, and also find a very good
agreement between measurements and model predictions.